This invention relates to AC plasma displays.
AC plasma displays are currently the subject of great interest as possible replacements for CRTs and for use in other applications requiring compactness and high resolution. Basically, such displays include a substrate and cover with a gap therebetween which enclose an ionizable gas such as neon or argon. Formed on the substrate is an array of electrodes (hereinafter "Y" electrodes) oriented in one direction, which array is covered by an insulating layer. Placed over the first array, either on the insulating layer over the substrate or over the cover, is a second array of electrodes (hereinafter "X" electrodes) extending in an orthogonal direction. This array is also covered by an insulating layer. Display pels are formed at the crosspoints of the electrodes of the two arrays. Pels are selected for display by application of an appropriate write pulse to the electrodes of the first and second arrays to locally ionize the gas and cause a luminous discharge. Charge will also collect on the insulating layers over the selected electrodes. By applying a lower amplitude AC sustain signal to all electrodes, the selected pels will remain in an "on" state as a result of the added potential provided by the collected charge which allows continued gas discharges in those areas. An appropriate erase signal can be applied to the selected electrodes to dissipate this charge and turn off the pel.
Recently, it has been proposed to provide displays with three or more electrodes per pel in order to simplify the write/arase and sustain circuitry (see U.S. Pat. No. 4,554,537 issued to G. W. Dick on Nov. 19, 1985 and assigned to the present assignee, which is incorporated by reference herein). In a basic embodiment of that invention, the Y electrodes comprise a plurality of pairs of electrodes arranged in rows with one of each electrode pair being electrically coupled in common while the other electrode in each pair is separately addressable. Each pel, therefore, comprises a pair of Y electrodes and an X electrode placed orthogonally thereto. A pel is selected for display by applying a write pulse to the separately addresable Y electrode and the orthogonal X electrode. Charge collected over the X electrode is then transferred to over the common Y electrode in the pel by application of a pulse thereto. The selected pels remain "on" by applying an AC sustain signal to both electrodes in each Y electrode pair so that the signals to each electrode in a pair have an opposite polarity and a magnitude such that they cause discharge of the gas only in the pels where charge has been previously collected. Appropriate erase signals can be applied in the sequence described above to remove charge in pels which are to be extinguished.
While such a display should be adequate for most applications, a potential problem exists if the Y electrodes are brought very close together to achieve higher resolution as might be necessary, for example, in color displays where three color pixels are used as each display site. In devices with high line densities, typically 100 or more lines per inch might be utilized and a spacing of 3 mils or less between adjacent electrode pairs may be needed. In such cases, it is possible for charge in an active (on) pel to be transferred to an adjacent inactive (off) pel during the application of the sustain signals. This undesired charge buildup could be sufficient to initiate a discharge in the inactive pel.
It is, therefore, a primary object of the invention to provide an AC plasma display which is capable of higher line densities and, therefore, higher resolution.